In the eXtremeDB, there is a term Node Quorum Rank refers to an integer value that is used to determine whether enough interconnected nodes are online to work. If the sum of the qrank values for node A and all nodes connected to A is more than half of the sum of the qrank values for all cluster nodes (online and offline), then node A (and other nodes online) will continue to work.
It is helpful to consider two node quorum rank example scenarios:
1. All nodes have the same qrank value: in this case the cluster will work if more than half of the nodes are active and connected to each other. If the cluster is split exactly in half, the cluster will not work.
2. One node (call it “main”) has a qrank value of 1, all other nodes have a qrank value of 0: in this case the cluster of nodes connected to “main” will always work. If the “main” node dies, the cluster ceases to work.
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